1. Field
Example embodiments relate to a normally-off high electron mobility transistor (HEMT), and more particularly, to a normally-off HEMT including a depletion-forming layer.
2. Description of the Related Art
Various power conversion systems may include a device for controlling a current flow by ON/OFF switching thereof, e.g., a power device. The efficiency of a power conversion system may depend on the efficiency of a power device in the power conversion system.
Many power devices commercialized at present are silicon (Si)-based power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) and Insulated Gate Bipolar Transistors (IGBTs). However, increasing the efficiency of a silicon-based power device may be limited by the physical properties of silicon, manufacturing processes, and so forth. To overcome these limitations, research has looked at using a group III-V compound semiconductor in a power device. In association with this, a high electron mobility transistor (HEMT) using a heterojunction structure of a compound semiconductor has attracted attention.
A HEMT may include semiconductor layers having different electrical polarization characteristics. In a HEMT, a semiconductor layer having a relatively high polarization rate may induce a two-dimensional electron gas (2DEG) in another semiconductor layer attached thereto, and the 2DEG may have very high electron mobility.
When a gate voltage of a HEMT is 0 V, power consumption may occur in a normally-on state in which a current flows between drain and source electrodes thereof due to a low resistance therebetween. To change to a normally-off state in which no current flows between the drain and source electrodes, a negative voltage may be applied to a gate electrode of a HEMT.
As another method, a HEMT having a depletion-forming layer to implement a normally-off characteristic by which no current flows between drain and source electrodes of the HEMT when a gate voltage thereof is 0 V has been researched.